Technical Abstract:
Biodiesel fuels (vegetable oils and animal fats and their derivatives, especially methyl esters) still pose some technical problems when used as alternative fuels in a diesel engine. One problem is the reduction of exhaust emissions such as NOx to meet increasingly stringent environmental regulations. NOx emissions are of particular concern because they are a precursor of ozone, a major component of smog. To solve the emissions problems, several aspects are being evaluated. Additives termed cetane improvers decrease NOx emissions in conventional diesel fuel. Cetane improvers having different effects on various fatty compounds are now identified, thus opening the possibility of tailoring the cetane improver to the predominant fatty compound in a biodiesel fuel. These effects depend on the nature of the cetane improver and structural features of fatty compounds such as number and position of double bonds as well as number of CH2 groups. In some cases, cetane number trends were altered. Compounds formed in the initial phase of fuel injection into the combustion chamber before ignition begins (precombustion phase) were evaluated by gas chromatography/mass spectrometry. Low cetane numbers of intermediary species formed prior to fuel ignition may be an explanation for differing cetane numbers of fatty compounds.